A cavity resonance phenomenon that occurs in an airtightly sealed tire cavity formed between the rim of a wheel and a pneumatic tire mounted on the rim is a major factor of tire noise. Noise around 250 Hz regularly heard during running or impulsive sounds generated in running over joint lines or the like of a road, for example, is involved with the cavity resonance phenomenon.
As a technique for reducing noise caused by such a cavity resonance phenomenon, there is known, for example, a technique such that a sound absorbing member of a porous material such as urethane resin foam is disposed on the inner surface of a tire facing the tire cavity to thereby reduce noise caused by the cavity resonance phenomenon (see a patent document 1, for example). On the other hand, the sound absorbing member has chipping and cracking arising from friction against the inner surface of the tire which is repeatedly deformed during running. Therefore, by increasing the density of the sound absorbing member, the mechanical strength of the sound absorbing member is enhanced to thereby suppress occurrence of chipping and cracking, enhancing durability.
However, mounting of the sound absorbing member with a high density increases tire weight, whereby an increase in unspring mass of the tire creates a problem of degrading ride comfort. Another problem is that it is difficult to obtain sufficient durability which can satisfy high requirements in the case of simply increasing the density of the sound absorbing member.    Patent Document 1: Japanese Patent Application Kokai Publication 2003-226104